This invention relates to linear polyesters of the aromatic, dicarboxylic acids terephthalic and isophthalic acid and 9,9-bis-(4-hydroxyphenyl)-fluorene. In a further aspect, it relates to a process for preparing such polyesters.
Interfacial polymerization methods can be desirable alternatives to solution polymerization methods because they may use less organic solvent thereby lowering solvent recovery cost, may provide shorter reaction times than solution polymerization methods, and may permit better control of reaction temperature because water can be a superior heat transfer medium to organic solvents. However, it has been noted that it may be difficult to obtain high molecular weight polymers using this method.
Polyesters of 9,9-bis-(4-hydroxyphenyl)-fluorene and isophthalic or terephthalic acid have been described in the art. U.S. Pat. No. 4,387,209 (Rieder et al.) describes polyesters made by reacting 9,9-bis-(4-hydroxyphenyl)-fluorene with at least one member of the group consisting of isophthalic or terephthalic acid using an interfacial polymerization process. However, Rieder et al. reported that at least some of the polyesters of their invention have a "binodal" molecular weight distribution wherein 10-20% of the polyester weight is comprised of low molecular weight species. Rieder et al. states that the presence of these species increases the adhesive qualities of the polyesters making them more useful in the electrical insulation field. Rieder et al. also teach that the inherent viscosity of the polyester is greatly dependent upon the purity of the monomer and that even relatively small variations in purity of the diphenol monomer can cause large deviations in the inherent viscosity values. Example 2 of U.S. Pat. No. 4,401,803 (Rieder) describes the preparation of polyesters of 9,9-bis-(4-hydroxyphenyl)-fluorene and a 50:50 mixture of isophthalic and terephthalic acid chloride using interfacial polymerization. He precipitates the polyester with an acetone-methanol blend to produce a material with an inherent viscosity of 1.67 dl/g. Neither oligomers nor low molecular weight species are mentioned. U.S. Pat. No. 4,533,511 (Mark) discloses a process for spinning fibers from the polycondensation product of 9,9-bis-(4-hydroxyphenyl)-fluorene and a mixture of isophthalic acid chloride and terephthalic acid chloride. He suggests dichloromethane as the spinning solvent and the liquid precipitant is preferably an aqueous lower alkanol. In one example acetone was used as the precipitant.
U.S. Pat. No. 4,066,623 (Besso et al.) discloses that certain aromatic, halogenated polyesters, which do not include the polyester of this invention, prepared by interfacial polymerization methods, will have bimodal molecular weight distributions. As a result, these polymers will contain a fraction (e.g., about 15 to 20% of the total polymer weight) of species with molecular weights not greater than 8000. Besso et al. states that the presence of these species results in solvent sensitivity of the polymer.
The importance of the molecular weight of the 9,9-bis-(4-hydroxyphenyl)-fluorene/isophthalic and terephthalic acid polyester (hereinafter, for brevity, occasionally referred to as the FPE copolymer) in achieving certain desirable physical properties has been discussed in the art. As noted above, Rieder et al. seems to view the presence of 10 to 20% of oligomeric species as producing an advantagous FPE copolymer property. It appears that only Besso et al. has contemplated, with respect to the polyesters described in their patent, that the presence of oligomeric species could undesirably effect polymer properties. Applicant was the first to note that even presence of small amounts (i.e., between 2 and 10% of total polyester weight) of oligomer species in the FPE copolymer can result in inferior properties. This is true even where the copolymer has a high average molecular weight or high inherent viscosity.
The applicant has determined that small amounts of oligomeric species in the FPE copolymer results in increased solvent sensitivity, lower elongation, poorer tensile strength, poorer chemical resistance, dimensional instability and variation in electrical properties when the material is exposed to high temperatures. Thus the presence of oligomer renders the FPE copolymer unsuitable for many applications such as those in which critical electrical properties must be maintained under high temperature conditions. Dimensional instability and chemical instability renders the material unsuitable for applications wherein the material is thermally printed. Applicant has further determined that the presence of even small amounts of oligomer will make the FPE copolymer sensitive to ultraviolet radiation and unstable under vacuum conditions. Films containing small amounts of oligomer will "yellow" or degrade upon limited exposure to ultraviolet radiation. This greatly limits the use of the film for applications in which the optical properties of the film are important, such as packaging material. Vacuum instability results in weight loss from the copolymer under vacuum conditions. This renders the material unsuitable for applications in which the material will be subjected to high vacuum conditions (e.g. 10.sup.-6 torr), such as applications where vapor deposition or sputtering processes are used.
Applicant has developed a novel 9,9-bis-(4-hydroxyphenyl)-fluorene/isophthalic and terephthalic acid polyester which contains a very low level of oligomeric material and possesses tensile strength, elongation, chemical resistance, temperature stability, ultraviolet resistance and vacuum stability superior to the FPE copolymers containing oligomeric species described in the art. Yet, applicant's copolymer has good adhesion to other materials such as metals having lost none of its "adhesive properties" despite the low level of oligomer present in the copolymer.